Autoradiograph

Applications

In biology, this technique may be used to determine the tissue (or cell) localization of a radioactive substance, either introduced into a metabolic pathway, bound to a receptor or enzyme, or hybridized to a nucleic acid. Applications for autoradiography are broad, ranging from biomedical to environmental sciences to industry.

Receptor autoradiography

The use of radiolabeled ligands to determine the tissue distributions of receptors is termed either in vivo or in vitro receptor autoradiography if the ligand is administered into the circulation (with subsequent tissue removal and sectioning) or applied to the tissue sections, respectively. Once the receptor density is known, in vitro autoradiography can also be used to determine the anatomical distribution and affinity of a radiolabeled drug towards the receptor. For in vitro autoradiography, radioligand was directly applying on frozen tissue sections without administration to the subject. Thus it cannot follow the distribution, metabolism and degradation situation completely in the living body. But because target in the cryosections is widely exposed and can direct contact with radioligand, in vitro autoradiography is still a quick and easy method to screen drug candidates, PET and SPECT ligands. The ligands are generally labeled with ³H (tritium), ¹⁸F (fluorine-18), ¹¹C (carbon-11) or ¹²⁵I (radioiodine). Compare to in vitro, ex vivo autoradiography were performed after administration of radioligand in the body, which can decrease the artifacts and are closer to the inner environment.

The distribution of RNA transcripts in tissue sections by the use of radiolabeled, complementary oligonucleotides or ribonucleic acids ("riboprobes") is called in situ hybridization histochemistry. Radioactive precursors of DNA and RNA, [³H]-thymidine and [³H]-uridine respectively, may be introduced to living cells to determine the timing of several phases of the cell cycle. RNA or DNA viral sequences can also be located in this fashion. These probes are usually labeled with ³²P, ³³P, or ³⁵S. In the realm of behavioral endocrinology, autoradiography can be used to determine hormonal uptake and indicate receptor location; an animal can be injected with a radiolabeled hormone, or the study can be conducted in vitro.

Rate of DNA replication

The rate of DNA replication in a mouse cell growing in vitro was measured by autoradiography as 33 nucleotides per second. The rate of phage T4 DNA elongation in phage-infected E. coli was also measured by autoradiography as 749 nucleotides per second during the period of exponential DNA increase at 37 °C (99 °F).

Detection of protein phosphorylation

Phosphorylation means the posttranslational addition of a phosphate group to specific amino acids of proteins, and such modification can lead to a drastic change in the stability or the function of a protein in the cell. Protein phosphorylation can be detected on an autoradiograph, after incubating the protein in vitro with the appropriate kinase and γ-32P-ATP. The radiolabeled phosphate of latter is incorporated into the protein which is isolated via SDS-PAGE and visualized on an autoradiograph of the gel. (See figure 3. of a recent study showing that CREB-binding protein is phosphorylated by HIPK2.)

Detection of sugar movement in plant tissue

In plant physiology, autoradiography can be used to determine sugar accumulation in leaf tissue. Sugar accumulation, as it relates to autoradiography, can described the phloem-loading strategy used in a plant. For example, if sugars accumulate in the minor veins of a leaf, it is expected that the leaves have few plasmodesmatal connections which is indicative of apoplastic movement, or an active phloem-loading strategy. Sugars, such as sucrose, fructose, or mannitol, are radiolabeled with [14-C], and then absorbed into leaf tissue by simple diffusion. The leaf tissue is then exposed to autoradiographic film (or emulsion) to produce an image. Images will show distinct vein patterns if sugar accumulation is concentrated in leaf veins (apoplastic movement), or images will show a static-like pattern if sugar accumulation is uniform throughout the leaf (symplastic movement).

Other techniques

This autoradiographic approach contrasts to techniques such as PET and SPECT where the exact 3-dimensional localization of the radiation source is provided by careful use of coincidence counting, gamma counters and other devices.

Krypton-85 is used to inspect aircraft components for small defects. Krypton-85 is allowed to penetrate small cracks, and then its presence is detected by autoradiography. The method is called "krypton gas penetrant imaging". The gas penetrates smaller openings than the liquids used in dye penetrant inspection and fluorescent penetrant inspection.